1. Field of the Invention
The present invention relates to an electric rivet nut tool, and more particularly to an electric rivet nut tool that automatically rotates a motor of the tool to release from a rivet nut after the completion of setting the rivet nut.
2. Description of the Related Art
When there is a need for multiple metal sheets to be joined and riveted, rivet nut is another choice to do the job in addition to nail or rivet. Rivet nut is tubular, is internally threaded, and penetrates through a hole formed through the metal sheets to be joined. Each rivet nut has a head and a body. The head is formed on and radially outwardly protrudes from a periphery of one end of the rivet nut. The body is tubular and internally threaded, is formed on the head and protrudes in a direction toward the other end of the rivet nub, and has a deformable portion formed on a free end of the body. An electric rivet nut tool rotates the body of a rivet nut through a nose piece engaging the internally threaded portion of the body of the rivet nut such that the deformable portion is deformed by a resulting shear and the deformable portion and the head of the rivet nut bind two sheet metals penetrated through by the rivet nut. When the rivet nut is set, the electric rivet nut tool automatically stops rotation of a motor thereof through a safety circuit loop and a forward/reverse button on the rivet nut tool can be manually switched to reversely rotate the motor and separate the electric rivet nut tool from the rivet nut.
From the foregoing, disadvantages of the conventional rivet nut tools can be listed below.                1. The forward/reverse button needs to be manually switched for the motor to forwardly rotate a rivet nut to a designated position and reversely rotate to release the conventional rivet nut tools from the rivet nut. Such manual operation consumes more time and is less efficient in operation.        2. As rivet nuts may be of different specifications, rivet nuts of different specifications need to be set with different torques. Higher torque may damage smaller rivet nuts upon driving them while lower torque may overdrive the motor upon driving larger rivet nuts. Hence, the life durations of the motor of the conventional rivet nut tools are shortened.        